Definitions for "Desert Varnish"
A thin, shiny red-brown or black layer, principally composed of iron manganese oxides, that coats the surfaces of many exposed desert rocks.
Black patina on the surface of rocks.
A gray or reddish-brown layer on rock surfaces that darkens and thickens with increasing age. Desert varnish results from microbial life processes that precipitate thin skins of clays and manganese oxide minerals. The thicknesses can be used to determine the amount of time the surface of a rock has been exposed. more details...